Radishes are funny things, they either like you or the alternative...
I could never, ever grow the things properly, but this year, I started sowing Annabelle F1 (Unwin) in trays, on a shelf in the GH, and they have romped away!
They seem to have adjusted to the extra heat, care and watering, and have really improved my faith in human nature - for once!
The seeds are big enough to sow separately, so I pop them in at inch and a half spacing, and for the first time in about three-hundred years, have the best results I could wish for!
Have a go, the seeds aren't cheap, but at least you'll get a reliable crop - even in a sunny spot outside if you are without a GH of course!
Best of luck!
(Lucky you, North Devon too)!